forked from boostorg/preprocessor
104 lines
3.8 KiB
HTML
104 lines
3.8 KiB
HTML
<html>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link rel="stylesheet" type="text/css" href="../../../../boost.css">
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<title>Boost.Preprocessor - Reference</title>
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</head>
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<body link="#0000ff" vlink="#800080">
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<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
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"header">
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<tr>
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<td valign="top" width="300">
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<h3><a href="../../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
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</td>
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<td valign="top">
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<h1 align="center">Boost.Preprocessor</h1>
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<h2 align="center">Header <<a href="../../../../boost/preprocessor/list/fold_left.hpp">boost/preprocessor/list/fold_left.hpp</a>></h2>
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</td>
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</tr>
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</table>
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<hr>
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<a href="list_first_n.htm">Prev</a> <a href="list_fold_left_2nd.htm">Next</a> <a href="index.htm#Macros">Macros</a> <a href="index.htm#Headers">Headers</a>
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<h3><a name="BOOST_PP_LIST_FOLD_LEFT">#define BOOST_PP_LIST_FOLD_LEFT</a>(OP,STATE,LIST)</h3>
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<p>Iterates <code>OP(D,STATE,X)</code> for each element <code>X</code> of the
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list <code>LIST</code> (from the left or the start of the list).</p>
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<p>In other words, expands to:</p>
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<pre>
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OP
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( D
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, ... OP(D, OP(D,STATE,<a href="list_at.htm#BOOST_PP_LIST_AT">BOOST_PP_LIST_AT</a>(LIST,0)), <a href="list_at.htm#BOOST_PP_LIST_AT">BOOST_PP_LIST_AT</a>(LIST,1)) ...
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, <a href="list_at.htm#BOOST_PP_LIST_AT">BOOST_PP_LIST_AT</a>(LIST,<a href="dec.htm#BOOST_PP_DEC">BOOST_PP_DEC</a>(<a href="list_size.htm#BOOST_PP_LIST_SIZE">BOOST_PP_LIST_SIZE</a>(LIST))
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)
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</pre>
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<p>For example,</p>
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<pre>
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#define TEST(D,STATE,X) <a href="cat.htm#BOOST_PP_CAT">BOOST_PP_CAT</a>(STATE,X)
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<a href="list_fold_left.htm#BOOST_PP_LIST_FOLD_LEFT">BOOST_PP_LIST_FOLD_LEFT</a>(TEST,_,<a href="tuple_to_list.htm#BOOST_PP_TUPLE_TO_LIST">BOOST_PP_TUPLE_TO_LIST</a>(3,(A,B,C)))
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</pre>
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<p>expands to:</p>
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<pre>
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_ABC
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</pre>
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<h3>Note</h3>
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<ul>
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<li>Folding, or accumulation, is a very general pattern of computation.
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Most list operations can be implemented in terms of folding.</li>
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</ul>
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<h3>See</h3>
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<ul>
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<li><a href="list_fold_right.htm#BOOST_PP_LIST_FOLD_RIGHT">BOOST_PP_LIST_FOLD_RIGHT</a>()</li>
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</ul>
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<h3>Test</h3>
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<ul>
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<li><a href="../../test/list_test.cpp">list_test.cpp</a></li>
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</ul>
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<hr>
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<h3><a name="BOOST_PP_LIST_FOLD_LEFT_D">#define BOOST_PP_LIST_FOLD_LEFT_D</a>(D,OP,STATE,LIST)</h3>
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<p>Can be used inside <a href="while.htm#BOOST_PP_WHILE">BOOST_PP_WHILE</a>() (see for an explanation of the D parameter).</p>
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<h3>Note</h3>
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<ul>
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<li><a href="list_fold_left.htm#BOOST_PP_LIST_FOLD_LEFT_D">BOOST_PP_LIST_FOLD_LEFT_D</a>() implements automatic recursion. You
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can use a fold in the OP macro.</li>
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</ul>
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<hr>
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<h3><a name="BOOST_PP_LIST_FOLD_LEFT_2ND">#define BOOST_PP_LIST_FOLD_LEFT_2ND</a></h3>
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<p>Obsolete, just use <a href="list_fold_left.htm#BOOST_PP_LIST_FOLD_LEFT">BOOST_PP_LIST_FOLD_LEFT</a>().</p>
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<hr>
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<h3><a name="BOOST_PP_LIST_FOLD_LEFT_2ND_D">#define BOOST_PP_LIST_FOLD_LEFT_2ND_D</a></h3>
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<p>Obsolete, just use <a href="list_fold_left.htm#BOOST_PP_LIST_FOLD_LEFT_D">BOOST_PP_LIST_FOLD_LEFT_D</a>().</p>
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<hr>
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<a href="list_first_n.htm">Prev</a> <a href="list_fold_left_2nd.htm">Next</a> <a href="index.htm#Macros">Macros</a> <a href="index.htm#Headers">Headers</a>
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<hr>
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<p>Revised <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %b %Y" startspan --><!--webbot bot="Timestamp" endspan i-checksum="15246" --></p>
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<p><i>© Copyright <a href="http://www.housemarque.com">Housemarque Oy</a> 2002</i></p>
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<p>Permission to copy, use, modify, sell and distribute this document is granted
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provided this copyright notice appears in all copies. This document is provided
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"as is" without express or implied warranty, and with no claim as to its suitability
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for any purpose.</p>
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</body></html>
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